Project Summary/Abstract Negative consequences of heroin use are not limited to those produced by the addictive qualities of the drug. Heroin and other opioids negatively alter host immunity, leaving users more susceptible to diseases commonly associated with heroin abuse. These immunomodulatory effects can become conditioned to environmental stimuli following repeated context-heroin pairings. The presentation of heroin-conditioned stimuli is sufficient to elicit pronounced suppression of peripheral pro-inflammatory measures in the absence of heroin itself. Through well-controlled animal models, our laboratory has demonstrated that heroin-conditioned immunomodulation is a classically conditioned response and follows the principles of learning. Consistently, the context-heroin association is governed through dorsal hippocampal (DH) processes. Within the DH, we have discovered that intact neuroimmune signaling is required for the heroin-conditioned peripheral immune response to occur. We have elegantly shown that both DH interleukin-1? (IL-1?) and its active receptor, IL-1 receptor type 1 (IL-1R1), critically mediate the expression of heroin-conditioned immunomodulation. To further investigate hippocampal neuroimmune involvement in this conditioned response, we employed state-of-the-art chemogenetic tools to selectively manipulate DH astroglial signaling in vivo. Stimulation of astroglial Gi-coupled designer receptors exclusively activated by designer drugs (DREADDs) during the exposure to heroin-conditioned stimuli disrupted conditioned suppression of peripheral immune measures. Thus, separately, DH IL-1 signaling and astroglial activity are necessary during presentation of heroin-paired cues to elicit the conditioned immune response. However, it is presently unknown if there is a mechanistic relationship between DH astroglial activity and IL-1 signaling in this Pavlovian response. There is evidence to suggest hippocampal astroglia support mechanisms of learning and memory through both IL-1? and IL-1R1. The current proposal is a targeted approach to investigate the relationship between DH astroglia and IL-1 signaling in heroin-conditioned immunomodulation. The specific aims test the overarching hypothesis that DH astroglia are a critical component of the IL-1 signaling necessary for heroin-conditioned immunomodulation. Aim 1 will examine astroglial-specific alterations in IL-1? and IL-1R1 mRNA and protein as a consequence of exposure to heroin-conditioned stimuli. Aim 2 will employ chemogenetic tools to selectively stimulate DH astroglial Gi-signaling during presentation of these heroin-paired cues to determine if this in vivo manipulation attenuates the IL-1? and IL-1R1 expression required for heroin- conditioned immunomodulation to occur. Collectively, the purposed experiments will enhance our understanding of critical neuroimmune mechanisms governing heroin-conditioned responses and will provide a valuable training opportunity to foster independence of my scientific career.